Russian opposition leader Alexei Navalny has vowed to continue to campaign against president Vladimir Putin despite suffering a chemical burn to his eye after a green liquid was thrown at his face.

Navalny, who is one of the fiercest and most prominent critics of Russia's president Vladimir Putin, was taken to hospital after being attacked by an unknown assailant outside his office.

In an online broadcast, he said: "At the exit from our office some weirdo splashed zelyonka at me. I didn't even understand what was going on. It got into the right eye.

Image:Alexei Navalny has vowed to continue his campaign against corruption

"I had to go to a hospital where I was diagnosed with a chemical burn of the right eye. Now I can open it with some effort, but you won't like what you will see. Therefore I won't do that."

It is the second time this year he has been attacked with zelyonka, a common antiseptic in Russia, which has been used in protests there and in Ukraine.

Image:Mr Navalny suffered eye burn in the attack outside his office

The liquid, also known as 'brilliant green', is sold in Russian pharmacies and while not harmful, it is known for being hard to wash off.

"It looks funny but it hurts like hell," Mr Navalny tweeted.

"Will it make us stop our activity or will we speak milder about people involved in corruption? Of course not, that won't make us do that.

Image:In an online broadcast, Alexei Navalny confirmed he had to go to hospital

"On the contrary, I think, we'll become angrier and I hope you will get angrier too, and will help us even more."

Navalny wants to run against Vladimir Putin for president next year, but is banned after being convicted of embezzlement last month, which would bar him from running for office, which he claims was orchestrated by the Kremlin.